Many devices for the above purpose are known, ranging from simple mechanical devices to rather complicated electrical or electronic devices. A good example of the latter category is the device shown in U.S. Pat. No. 5,253,735, which is regarded is the closest prior art. Here, three discs, which are rotatable relative to each other and are arranged on the cam shaft adjacent the brake lever, are provided with magnets and hall-elements in a certain arrangement for supplying certain information about the condition of the brake.
The basic function of a device as defined is to supply information about the wear of the brake linings, so that they can be replaced in time, and accordingly the name wear sensor may be used. However, a wear sensor properly designed and installed can also supply useful information about the piston stroke of the brake cylinder used and about the overall function of the brakes on the vehicle.
It is of great importance that a wear sensor is sturdy and can resist the extremely harsh environmental conditions under the vehicle. The sensor shall also have small dimensions due to the often very limited available space. The information provided from the sensor shall be as accurate as possible and shall be compatible with other information available in modern vehicles, where computers and other electronic equipment are used to an increasingly large extent.